The last line is saying that the order the individual records are deleted is not defined. So if you have a table with ids of 1, 2, 3... Then "delete from tbl order by id limit 5;" will delete id's 1 through 5. The last paragraph is saying that it might delete those individual rows in the order 3, 5, 1, 4, 2. So the ORDER BY was used to determine which rows will be deleted, but it doesn't actually say: delete row 1... then delete row 2... then delete row 3... etc.